The field of this invention is anchor systems for well tools and, more particularly, high expansion bridge plugs or packers.
Well tools frequently need to be anchored in casing for proper operation. In situations where the tool has to be delivered through tubing and set in casing, the anchor assembly must extend substantially from the run in position to grab the casing. This happens because the tool must be no bigger than a small dimension to be run smoothly through tubing and yet must expand substantially in percentage terms to grab the casing. In the case of a plug or packer, substantial directional forces are transmitted to the anchor system when such tools are set.
The designs of anchor systems in high expansion service have shown limited abilities to retain grip and some have released their grip under load. Generally these designs involve a release when the wickers on the end of a link that contacts the casing simply shear and the grip is lost. In the past, high expansion anchor systems involved rotating individual links that engage the casing with wickers mounted on an end. Examples of this design are U.S. Pat. Nos. 6,311,778 and 6,318,461. A through tubing design using similar anchor assemblies is shown in U.S. Re 32,831. In applications where high expansion is not an issue, the known technique of pushing slips out with cones has been employed, as shown in U.S. Pat. No. 6,220,348.
The problem with past designs is that they had a limited grip area due primarily to their layout of having wickers at the end of a thin link engage the casing wall. Even though multiple links would get independently actuated around the periphery of the packer or plug, the links were narrow and their grip limited for that reason. Even a plurality of such individual links could not support a tool in extreme loading conditions. What is needed and provided by the present invention is a way to increase the bite area of the gripping member that engages the casing wall. This has been accomplished in part due to the placement of the gripping member at the intersection of a plurality of links as well as controls built into the linkage to control the final movement of the gripping surface. Provisions for pin connection failure have been made so that the anchor of the present invention could still retain a grip if such a connection weakened or failed under heavy load. These and other advantages of the present invention will be more apparent to one skilled in the art from a review of the description of the preferred embodiment and the claims below.
An anchor system for high expansion applications is described. It features a gripping member that holds together a pair of links. The movement of the links is regulated to assure the gripping member moves into proper contact with the casing. Meshing gears or a pin and slot can do this, for example. The gripping member is shaped such that it can still transmit load through the links even if the pin connections fail. The gripping member is preferably contoured to the shape of the casing inner wall to enhance grip.